1. Field of the Invention
The present invention relates to that gathers permeability measurements of a fabric preform for use in a liquid composite molding process after situation of the preform within the mold wherein the molding process is to occur.
2. Background of the Prior Art
Fiber reinforced composite materials are an important class of engineering materials that offer outstanding mechanical properties and unique design flexibility. Such materials are lightweight, corrosive resistant, impact resistant and exhibit excellent fatigue strength. Composite materials are used in a wide variety of applications including automotive parts, aviation, marine vessels, offshore structures, containers and piping, and sporting goods among others. Liquid composite molding, which includes resin transfer molding, reaction injection molding, and resin infusion, is one of the most attractive manufacturing solutions to producing high quality, affordable, and environmentally friendly composite materials.
Recently, a considerable amount of progress has been achieved for liquid composite molding techniques such as constituent material development, tooling, reinforcement preform development, curing control, and process simulation. These advances have lifted the liquid composite molding process to new heights.
However, a major barrier has retarded the advancement of liquid composite molding, the barrier being the reproducibility of the finished part, which tends to be lower than expected resulting in higher than expected manufacturing costs of the finished products actual manufactured and accepted.
In the liquid composite molding process, resin flow induced defects are recognized as the largest source of quality and reproducibility problems. The resin flow pattern is strongly related to fiber preform layup and mold fit. In a liquid composite molding process, poor raw material (fiber) quality or improper fiber preform preparation often result in local permeability variations. These permeability variations can lead to unbalanced resin flows, which in turn , produce defect parts.
Permeability, which characterizes the flow resistance of the fiber preform to the liquid resin in the liquid composite molding process, is widely used in liquid composite molding applications as one of the most important process design and control parameters. If serious permeability variations and misfit between the preform and the mold exist, defects will result in the resin low field, which leads to defective finished parts.
Current methods for testing the permeability of the preform use specially designed molds that measure the pressure and flow rate or flow distance of the resin to obtain an average permeability using Darcy""s law. The problems for arriving at the permeability of the preform using the existing method are twofold. First, the method only delivers the average permeability of the preform. It does not measure local permeability variations of the fiber preform due to inherent raw material variations as well as improper preform loading. Second, the permeability measurements are conducted off-line. As the preform is a flexible structure, it is easy to deform and restructure during the handling process. When the preform is laid up in the production mold, significant changes in the preform permeability can be realized due to fiber deformation and mold misfit. Accordingly, the measured permeability may not represent the true value of the permeability of the preform in the production mold.
Therefore, there is a need in the art for a system for use in the liquid composite molding process that overcomes the above-stated problems in the art. Specifically, such a system must allow for a high level of reproducibility of the finished part manufactured using the liquid composite molding process. In order to achieve this high level, the permeability of the preform needs to be measured across the entire preform after situation of the preform within the actual mold wherein the liquid composite molding process upon the preform will occur so that preform fabric defects and/or mold misfits can be detected prior to the commencement of resin flow. Ideally, such a system will be of relatively simple construction and will be relatively easy to use and will not have adverse effects upon the finished product.
The system for in-situ and on-line monitoring of a preform layup process for liquid composite molding of the present invention addresses the aforementioned needs in the art. The system allows for gathering of permeability measurements of a fabric preform for use in a liquid composite molding process after situation of the preform within the mold wherein the molding process is to occur. The system can be used to create a pressure profile, a contour profile, or can be processed in any other fashion desired by the user. From such data, any local permeability measurements that are caused from defects in the preform, deformation of the preform, or from mold misfit can be noted and acted upon before resin flow. The system is relatively simple to use and is easy to implement.
The system for in-situ and on-line monitoring of a preform layup process for liquid composite molding of the present invention is comprised of a mold that has an upper section and a lower section forming a cavity therebetween and has an inlet port and an outlet port. A plurality of openings are located within the lower section while a plurality of pressure sensors are each attached to a respective one of the plurality of openings. A source of compressed gas is fluid flow connected to the inlet port. Each pressure sensor can be attached to its respective opening via an adapter which adapter can be operable between an open position wherein fluid flow communication between the pressure sensor and its respective opening is present and a closed position wherein fluid flow communication between the pressure sensor and its respective opening is absent. The pressure sensors may be MEMS pressure sensors. Each pressure sensor is connected to a data acquisition and processing device. which can be a computer. A reject hole located within the mold and a pin hole may each be located within the mold. A flow meter may be fluid flow connected with the inlet port, the flow meter also be connected to the data acquisition and processing device. A resin pump fluid flow is connected to the inlet port and may be fluid flow connected with the flow meter. The gas within the source of pressurized gas may be nitrogen.